Electronic control for contour milling machines



G. F. KELK ELECTRONIC CONTROL FOR CONTOUR MILLING MACHINES Oct. 13, 1953 4 Sheets-Sheet 1 Filed Jan. 29, 1949 INVENTOR G. F. KELK ATTO RNEY Oct. 13, 1953 Filed Jan. 29, 1949 TRACER/1 UNIT G. F. KELK ELECTRONIC CONTROL FOR CONTOUR MILLING MACHINES BRIDGE 138 NETWORK 4 Sheets-Sheet 2 CONTQOLJ 43 Mb OVER- RIDNG THYQATON coN'rRoL um'r pl LOT GEN EEATOR FEED MOTOQ.

5 \G a K W INVENTOR G. F KELK AT'TCR EY Oct. 13, 1953 G. F. KELK 2,655,630

ELECTRONIC CONTROL FOR CONTOUR MILLING MACHINES Filed Jan. 29, 1949 4 Sheets-Sheet 3 TOCLUTCH RELH Y5 HQ UNV T COVEPl Firs.

'INVENTOE G. F KELK A'rronwav 4 Sheets-Sheet 4 TORNEY GEAR 136)? MOVING TABLE G. F. KELK MOTOR Oct. 13, 1953 ELECTRONIC CONTROL FOR CONTOUR MILLING MACHINES Filed Jan. 29, 1949 TQAVERSE MOTOR Patented Oct. 13, 1953 nnncrnonlc1c0NTaoL FoR CONTOUR 711mg MACHINES .r v.

;(3; e )rg e Kelk, Leaside, "-Qntario, Canada, as-

' Gama;

wtonA. V qe Qanada Li'mitedg'Malton,

corporation Application Janual y 29, 194?, Serial-Nor 73,567 5i (l lainls. (01.321 16) .This invention melatfis rgenerallyito thecontrcl of contour .millingmachines, ;or iofq similar 116.- production devices; by meansqof a: tllflCfiIZ-Ofyffll- :lowenmoving over aipatternof theiarticlewhich theamachine. is; to.. reproducenand more; particularlyitirelates toean electronic variab ccapacitance follower .-f0ruseriwith icontoturt. milling Ana.- chines.

.An objectiofthisinvention-is to ,providaa gery -sensitivewa-ndv simple control which w-ill not damage the-pattern by exerting a heavcv flloadv ll-ppllzl Anothenobject t is; to provide a follower which will be rapid andtsmcpthi op rat on; an whi h :Will tenable the mattern t e accurate rep einduc d I so that the. repr dnctigntwii1 .Arequi-re a minimum of surfac fin s in afte th -pr mary mil-ling :operation.

Still a furth r -ebiec.t o thi nvent i t p ovide a new and t-timpmved t pe 1 at at c tracing ntrolghea wh r i asMn tarr-wnstruw 1 tiOn-Of-a highr equ nc o cillato n ca aci iv couplin ele ents. ont ined n elyisw t in th trac n h a provide control tvo te e td rectl ith u -nee e com le -brid t iba ea ns ni cuits external thereto.

' n, is well known, of course, thQt QIBQlZl'lQ controls for automatic contouring n achines been in industrialuse for sometime.

ample of such equipment, 'illnst rating quitewell ,the present state of the' art, is "described in an article entitled Machine-toot hen controller by -J -Morgan in Electronics-Maazine," October 1946, -page 92- (McGraw-Hill) The prior art tracing controls-have ingeneral .followed. the principle oftprovidingisome member in .a; tracing head; andisecuredg .tora stylnsaasta comp n nt lem t of .i a .mpedanc abridge. w c vme a ul tonieined ts d th tracin head. In the constrnction descrihed -in the aforementioned article-.theelernents are a inatt ures of .magnetic circuits. Invother I equipment, the elements are variable capac o rs, or magnetostrictivedevices. They are. prowided, in, some form or other, as constituents ofanelectrical bridge, and-the stylusdefiectionsfoperate bridge.

=The -invention disclosed and claimed therein departs. from:- thesetteachings andemakesinsemof :intermediate. capacitive members .ldisposedj along n a neutral plane in. ahigh frequency electr c field as: the, styluscdeflection sensingielement. 'IT-he vhigh frequency'yoltagesiinducediqn :the members, when stylus defiectionsziforce {them out et; their through'the element to upset the balance of the neutral planes; are. rectified, and nrovide -nniqigrectional control voltages. The capaeitiy e umembersthus form, a differential condenser; one side ,decre ases in .c apacitance as the other'in creasesy iving a linear ontput against deflection, even for large deflections, and inherentl yfprovides compensationifor drift due to changesiin ,icapacitance from any-causes other than stylus deflection. Theseadvantages are not found in tanytracer in whichonly one arm of themeasuringv bridge is varied by 4 the controlling signal;

In accordance with apreferred embodiment of this invention, the high frequency electric field is o c h me ns of @pp e ereeitirl t-piates eonne tedt cppps t end ra -i d ct- ,ancecoupled to an;electronieoscillator. The neutral electric plane is established rnidj qay between the opposed plates avith reference r t o a center-tap on the inductance. Furthermore,

.thereare provided three pairs; of opposed Canaditivei plates orthogonal or mutually perpendicw tlaritoweachother, and a cascade rectifying circuit ,is, used to integrategthe Voltages resultingifroni deflection of the stylus in any directionintaa single control ,yoltage, which, through suitable apparatus, operatesto withdraw the tracing head and. stylus rom. the temp or patternjthereiiy :relieving the pressure; on the; stylus.

.B y jt hi i nst uct n th sen i t o tim .econtroL; has v been so greatly: improved -that it; is

now possible to cut, ,by automatic contouring,

steel reproductions of delicate plaster .patterns, .-with 7 maximum dimensional .deviations .of ,no

gr ater than a ;few thousandths of an 11inch.

-,Moreoyer,l,in comparison with variable inductvlance pick ups, usuallyphaving iron cores, his i construc on odiesa v es em O lower ,mes qu ri et la i el l h us' e 0'1 DllfitOgthj-S feature the stylusfexerts biitfa vwounces of pressure onthe pattern; so it may be ,made of a relatively soft material-such ,Vplaster with no appreciable wear thereon. thought that no snch results have ever bee n achieyed; with prior art equipment.

:Still further objects and advantages of the invention will become. apparent; durin th QQ ZSe :of thefollowing.description, of a. preferred em- -.bodiment.of:the same wherein like numerals-are 3 portions of the control mechanism of a contour milling machine;

Fig. 4 is a circuit diagram of a. tracer unit and control unit showing a typical application of the fundamental principles of this invention;

Fig. 5 is a diagrammatic representation of a tracer unit and a milling cutter in contact with a pattern and workpiece, respectively, on the machine, and

Fig. 6 is a simplified circuit diagram of a tracer unit, arranged to provide an independent output E. M. F. from each of the three senses of deflection of the unit so that more than one of the operating motors may be automatically and simultaneously controlled.

With reference to Figs. 1 and 2 it will be seen that a tracer constructed in accordance with this invention comprises a casing I from one end of which extends a pressure sensitive portion in the form of a stylus B and within which are housed there variable split-stator condensers 9, H3 and H. The stylus s and the centre plates of the condensers s, it and H are mounted by means of insulating washers on a quill 12 which is sup ported at its forward end by a spring diaphragm l3 and at its remote end by a retaining spring Hi. The quill i2 is rigid and any movement of stylus 8 is thereby transmitted to the variable condensers ii, iii and l I. To avoid damage in the event of failure of any part of the electronic control, safety contacts comprising spigot l5 and plate It are provided; these close on excessive deflection of the quill, thereby causing disengagement of the magnetic clutches which control the application of electrical power to the traverse,

indexing and feed drives of the machine.

Spigot I5 moves in hole it in plate Hi, the diameter of said hole being substantially greater than the diameter of the spigot, but smaller than the diameter of shoulder l5 on spigot It. The safety circuit is made when the spigot is displaced sumciently to bring it or its shoulder into contact with plate l6.

The spring diaphragm l3 supports the quill l2 at the point of balance of the latter to eliminate lateral deflections due to vibration of the machine on which the tracer is mounted. In other respects the diaphragm l3 acts as a universal pivot and allows the stylus 8 to have a limited degree of movement in all directions.

The condenser 9 consists of three plates or discs which are preferably circular and mounted concentrically with, and transversely of, the the tracer unit axis. The outer annular stator plates l1 and IQ of condenser 9 are fixed to, but insulated from, body IQ of the unit, as shown in Fig. 1, the axial holes in the stator plates providing sufiicient clearance for quill [2 which passes therethrough. The third plate is disposed between plates I1 and i8 and on quill l2 as previously described. Condensers Hi and H each comprise four plane parallel rectangular plates, the outermost two of which are fixed longitudinally to body :9 of the unit, but insulated there from, while the innermost two are secured to quill l2. Electrically each pair of intermediate plates mounted on the quill may be regarded as one plate, since they are connected to each other by brass mounting screws extending therebetween. Condensers l0 and H lie in orthogonal planes, that is, planes perpendicular to each other and mutually perpendicular to the plane of the condenser 9.

During assembly, axial alignment of the quill is eifected by means of an adjustable anchorage of spring !4 as seen particularly in Fig. 1. This anchorage comprises plate 2| to which the spring is fastened, angle bracket 22 secured to body i9, screws 23, washer plate 24 and spring steel lock washer 25. The holes in angle bracket 22 are oversize, thereby permitting a certain amount of lateral adjustment in order to achieve a satisfactory degree of axial alignment.

After having adjusted the position of quill 12, as described in the preceding paragraph, it is necessary to balance the condensers l8 and II electrostatically and for this purpose two small fixed condensers 28 and 2'! (see Fig. 4) and two small adjustable condensers 26 and 21 are provided, the latter being arranged for convenience of adjustment adjacent condenser H. The adjustment of condensers 26 and 2'! will be subsequently described.

The tracer unit also houses an oscillator tube 28, which supplies through centre tapped transformer 29, a high frequency voltage of the order of 600 kc./s. to the aforementioned condensers. The ends of the secondary winding 29 are con nected to the outer plates of each of condensers 9, l8 and I I. Hence, if the electrical capacitance between one of the outer plates and the corresponding inner plate of any one of the condensers differs from the electrical capacitance between the other outer plate and the said inner plate hi h frequency voltage will exist between the inher plate, and the centre tap of secondary winding 29 More strictly speaking, the outer or opposed capacitive plates establish a high frequency electric field, wherein the intermediate plates, when disposed midway between, lie in a plane which is electrically neutral with respect to the center-tap of transformer 29. Any movement of the intermediate plates out of their neutral plane causes a high frequency voltage to be generated thereon with respect to the center tap. It should be evident that since an appreciable E. M. F. ought to exist between any one of the inner plates of condensers 9, l0 and H and the centre tap only when the stylus is deflected, balancing condensers 26 and 21 are provided between one outer plate and the inner plate, for adjustment of condensers ID and ll respectively. (It will be subsequently shown that no such arrangement is necessary in the case of condenser 9.)

In the preferred example condensers 2 3 and 27 are adjustable metallized ceramic condensers. These have suificient capacitance, even at the minimum setting, to unbalance the electrical circuit. Therefore fixed condensers 26 and 21, each having a capacitance roughly one-half that obtainable in condensers 25 and 21 are connected between the other outer plate and the inner plate of each of condensers l8 and II re spectively. Thus by suitable adjustment of condensers 26 and 21 a fine degree of balance may be achieved between the inner plates of condensers l9 and H and their outer plates so that when stylus 8 is undeflected, the E. M. F. between the inner plates and the centre tap of winding 29 will be negligible. Germanium rectifiers 33, 34 and 35 with their associated choke coils 30, 3| and 32 and filter condensers 33 3 and 35 constitute a series or cascade rectifying circuit, somewhat similar to the voltage doubling circuit well known in the electronic art, which converts the output voltage from the balanced condensers due to deflection of the stylus in any direction into a undirectional voltage for the controlof the 'ini lling operation, description of which follows:

as previously stated, stylus 8 protrudes lrom one end of casing l, and a se'ven' p'in plug "3! is mountedon the opp'osi-te'end. This plug carries "the heater voltage and unidirectional voltage input to the oscillator tube 2-8, the "safety -c'iroint and the unidirectional voltage output-of th'e rectifiers in the tracer unit.

From Figfi =it W-i1l besee'n that the out-put from the tracer unit is fed to a d-i rect coupled amplifier 38 which also contains an '--overriding manual control 43 or the machine. "The control voltage from the amplifier 38 together with "a til xiiiirec'tiorial bias voltage, manually controlled byititii-tioriietr 43,*is fed to a "thyratron'moto'r oontrol unit B-B'Whic-hin turn suppuesth power to direct current "shunt -motor 4B, the magnitud'e and =po1arityof the voltage of which is a direct iun'ction or the magnitude and polarity of the oontrol voltage from unit 38. 'Motor-Ml, the "Speedof which is closely proportional to the-contro'l voltage, drive table 41 on which the work "is mounted, as shown in Fig. 5, and the rate of feed, i.'-e., the speed "at which table moves the direction of the arrow M is "governed -thereby. Pilot generator 12 is directly coupled *to'rnotor MI and operates to supply alarge degree ofinverse feedback to the input of thyratron unit "39 to ensure close conformity between the *speed of the motor It and the control voltage, regardless of load 'Thisinverse feedback method of mechanical stabilization of rotating electrical finachi-neryfis well known in the art .and need not *be further described. v v From the electrical circuit of'the follower and controlunit shown in Fig. 4 it will be seen that =thecontrol unit comprises a double triode, one "section of which amplifies the output voltage from the "tracer unit, and which,'combined with the second triode section and with the anode load resistors, forms a Wheatston'e bridge. This bridge is balanced through amanu'a'lly opera'teld control 43 which in effect determines the basic magnitude and polarity of the controlvo'lta'ge fed to the thyratron power feed control tubes.

fFig. '5shows the tracer stylus 8 contact with {a pattern 4'4, and the milling "tool 15 in contact with awork piece 46. The tracer unit 'an dthe tool'liare mounted rigidly'on the framed! of the'mach-ine, while the pattern 44 and work-- piece 46 are mounted on the movable table '41. The table is traversedat a constant speed'inthe jiirection of arrow 4|, and simultaneously it is fed toward stylus 8 and tool 5 in the direction of the arrow M by the motor 40, .as hereinbefo're described. Indexing occurs at the end of each traverse so that when the machine repeats its -traverseit will follow a path displaced laterally 'a'small .amount from the previous path taken. The tracer unit provides a voltage which increases with'pressure exerted on stylus 8 in any direction, by virtue of the arrangement of con- :densers 9 l0 and H in three'mutually perpendicular planes. For example, direct .axialpressure on styIusiBnefiects spring diaphragm 1'3 inwardlyand causes an axial displacement of the central plate of th'evariable'condenser 9 to- "ward flxed'plate I8. "As previouslydescribed,the {oscillator i l'p'rovides a high frequency electric field between the condenser plates'so that any "movemen't'of plate Ill-towards plate -18 decreases the capacitive reactance between plates i8 and "in and increases thebap'acitive reactance between Iilates l and "-20, thereby increasingthe notch-- iby cutter pressure.

applied to its armature andso said speed and direction th'ereiore vary a n function of i the 'pl'if-ler output voltage at terminal-m, :r "The- 6pe'iation 'of "such thyr'atron control "units is com- -'m"on knowl'edge in the art andtherefore need-not be "further described.

ns-thepattern 44 is broughtagainst stylus 8 and beginsto press "upon it, a voltage is pro- {duced which, at a certain pressure exerted the pattern on the stylus, exactly balances the voltage initially applied to feed motor 40 by the manual adjustment of control 43. 'When this balanceoccurs th'emotor-stops. Any further increase in pressure due to a rising slope of the pattern contour in the-direction of traverse I P, willcansethe'voltage from the amplifier to increase again but its polarity is opposite to "that of the original -'-bias voltage as set by "control "43.

so that motor 40 is made toreversa'thereby withdrawing table 41 andwith it workpiece -46 irom fthe cutter until balance again is restored. Similarly, anydecrease in pressure due to a'dip in the pattern contour in the direction] I, will cause the motor lll'to start running ,againin its original sense until balance "is again restored. It will be understoodtherefore that the pressure on stylus 8 necessary .to'achieve "balance is dependent "upon the bias voltage, the latter "being manually applied and remaining constant throughout'ithe entire imilling operation. Theoretically any degree of sensitivity and accuracy of reproduction can'be ,obtainedlby this-means, r but-in practice aLstylus deflection must be'us'ed which is -.greaterithan .the relative movement between the tracer andithe pattern, vdue'to yibration and deflection of the machine .frame caused This requisite .haslresulte'd in the use of a stylus pressure of ibetween two to four ounceswhich is still sufiiciently smallthat evenplaster pattern can be used time after time WlthOlltvGXCGSSlVG wear or deterioration of the surface. Previously to this invention, plaster patterns could not be .usedat all .since thestylus .pressuresapplied by the known types of followers which were of the order of two to three pounds, 'weresufflcient ito :destroy'the surface of the patternb'y thetime-thefirst ;few passes by the stylus ihadabeentmade.

1n the preceding paragraph,axiahdisplacement of '.:stylus :8 was considered as 'anexample, but

lateral displacement acting upon "condenser or =;l:l will produce a similar effect, and in fact,

sincethe unidirectional output voltageslfrom rectifiers E33 31 and 35 are arranged in series or cascaded .by means-of :chokes 3i and.32,.as,s ho.wn in Fig. 4, the effects of lateral and axial displacement.are.electricallyoresolve'd to producea resultant control voltageirom thetracer unit themagnitude of".which is their algebraic sum. "Since it 'is' possible that the central plates of condensers IO and H may be displaced in either' direction, it is important that these condensers should be accurately balanced electrostatically when the stylus displacement is zero. This may be efiected by means of adjustable condensers 26 and 21 as previously described. In the initial assembly of the tracer unit the central plate 20 of condenser 9 should be so adjusted that it is situated at least as close to plate 18 as to plate IT in the mechanically neutral or no deflection position, and therefore, since only a positive pressure can be applied axially to stylus 8 (i. e. the stylus cannot be subjected to a pull), the necessity of a balancing condenser is thereby eliminated.

It is to be understood that the form of this invention herewith shown and described is to be taken as a preferred example of the same, suitable for the contour milling of comparatively simple shapes in which the displacements of the stylus in three dimensions can be translated into a single control voltage, which operates to withdraw the work-piece from the tool regardless of the direction or combination of directions in which excessive pressure on the stylus occurs. If it is desired to employ a more exact form of contol in which the displacements in different di rections are to be treated independently, for example, in profiling with constant feed rate, then a tracer unit wired as depicted in Fig. 6 may be employed. In this arragnement high frequency output voltages 41, 48 and 49 from each of the three balanced condensers 9, l and H are supplied separately to three separate rectifier and amplifier control units.

opposed plates of respective pairs along planes 1 electrically neutral with respect to said centertap, deflection of said stylus in any of said orthogonal directions causing movement of corresponding ones of said intermediate plates out of their respective neutral planes and the induction of high frequency voltages thereon with respect to said center-tap, and a plurality of rectifying means connected between said intermediate plates and said center-tap for providing unidirectional control voltages proportional to said induced high frequency voltages for each of said orthogonal directions.

2. A pressure responsive device comprising a housing, a stylus resiliently mounted thereon and adapted to deflect through limited ranges in orthogonal directions in response to pressure,

a plurality of pairs of opposed insulated capacitive plates rigidly mounted in said housing in orthogonal dispositions, a center-tapped inductance connected across said pairs of plates in parallel, an electronic oscillator coupled to said inductance for establishing high frequency electric fields between opposed plates in said pairs, a plurality of intermediate capacitive plates secured to said stylus and medially disposed between said opposed plates of respective pairs along planes electrically neutral with respect to said centertap, deflection of said stylus in any of said orthogonal directions causing movement of corresponding ones of said intermediate plates out of their respective neutral planes and the induction of high frequency voltages thereon with respect to said center-tap, and a plurality of rectifying means connected between said intermediate plates and said center-tap, said rectifying means being connected in a cascade circuit for integrating the unidirectional control voltages corresponding to movements of said stylus in any of said orthogonal directions into a single unidirectional control voltage.

3. A pressure responsive device comprising a housing, a stylus resiliently mounted thereon and adapted to deflect axially and laterally through limited ranges in response to pressure, three pairs of opposed capacitive plates rigidly mounted in said housing, one pair being normal to the axis of said stylus and the two other pairs normal to each other and parallel to said axis, a centertapped inductance connected across said pairs of plates in parallel, an electronic oscillator coupled to said inductance for establishing high frequency electric fields between opposed plates in said pairs, three intermediate capacitive plates secured to said stylus and medially disposed between opposed plates of corresponding pairs along planes electrically neutral with respect to said center-tap, axial or lateral deflections of said stylus causing movement of the corresponding intermediate plates out of their respective neutral planes and the induction of high frequency voltages thereon with respect to said center-tap, and a plurality of rectifying means connected between said intermediate plates and said centertap for providing unidirectional control voltages corresponding to said deflections.

4. A pressure responsive device comprising a housing, a stylus, an elongated quill member holding said stylus, means including a diaphragm at the stylus end and a spring at the opposite end of the member supporting it and enabling it to deflect axially and laterally through limited ranges in response to pressure on said stylus, three pairs of opposed capacitive plates rigidly mounted in said housing, one pair being normal to the axis of said member and the two other pairs normal to each other and parallel to said axis, a center-tapped inductance connected across said pairs of plates in parallel, an electronic oscillator in said housing, including an oscillatory circuit coupled to said inductance for inducing high frequency oscillations therein and establishing high frequency electric fields between opposed plates in said pairs, three intermediate capacitive plates secured to said member and medially disposed between opposed plates of corresponding pairs along planes electrically neutral with respect to said center-tap, axial or lateral deflections of said member causing movement of the corresponding intermediate plates out of their respective neutral planes and the induction of high frequency voltages thereon with respect to said center-tap, and a plurality of rectifying means connected between said intermediate plates and said center tap for providing unidirectional control voltages corresponding to said deflections.

5. A pressure responsive device comprising a housing, a stylus, an elongated quill member holding said stylus, means including a diaphragm at the stylus end and a spring at the opposite end of the member resiliently supporting it and enabling it to deflect axially and laterally through limited ranges in response to pressure on said stylus, three pairs of opposed capacitive plates rigidly mounted in said housing, one pair located 9 next said diaphragm being normal to the axis of said member and annularly disposed relative thereto and the two other pairs normal to each other and parallel to said axis, a center-tapped inductance connected across said pairs of plates in parallel, an electronic oscillator in said housing, including an oscillatory circuit coupled to said inductance for inducing high frequency oscillations therein and establishing high frequency electric fields between opposed plates in said pairs, three intermediate capacitive plates secured to said member and medially disposed between opposed plates of corresponding pairs along planes electrically neutral with respect to said center-tap, axial or lateral deflections of i said member causing movement of the corresponding intermediate plates out of their respective neutral planes and the induction of high frequency voltages thereon with respect to said center-tap, and a plurality of rectifying means connected between said intermediate plates and 10 said center-tap, said rectifying means being connected in a cascade circuit for integrating the unidirectional control voltages corresponding to axial and lateral deflections of said member into a single unidirectional control voltage.

GEORGE F. KELK.

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